Modular aptameric sensors for oligonucleotides were constructed by combiningmolecular beacon stem-loops andmalachite green aptamers. These sensorswere designed so that oligonucleotides complementary to the stem-loop region accomplish the release of malachite green from its binding module. The oligonucleotides that bound to both loop and stem caused efficient release of the dye. While this system is not suitable for single-mismatch detection, it represents proof-of-concept for drug delivery components of autonomous therapeutic devices on a molecular scale.